1. Field of the Invention
The present invention relates to a copper alloy and to a process for producing the same. More particularly, it relates to a copper alloy used as a lead frame material for semiconductors such as IC and LSI and to a process for producing the same. The lead frame material for semiconductors is superior in strength, stiffness strength, repeated bending characteristics, heat resistance, and electrical conductivity.
The present invention also relates to a copper alloy for terminals and connectors and to a process for producing the same. The copper alloy for terminals and connectors is characterized in that the electrical conductivity is at least 25% IACS and 80% of the initial hardness is retained even when heated at a temperature above 400.degree. C. for 5 minutes.
2. Discussion of the Background
Heretofore, the lead frame materials for semiconductors have been made of Fe-42 wt% Ni alloy which has a coefficient of linear thermal expansion close to that of the elements and ceramics. However, with the recent improvement in bonding technique and sealing materials for the elements, it is being replaced by copper-based material which is superior in heat dissipation and yet is comparatively low in prace.
Nevertheless, there are no copper-based materials developed so far which have superior strength, repeated bending characteristics, and heat resistance comparable to those of the Fe-42 wt% Ni alloy and are suitable for the lead frame material for semiconductors such as IC and LSI which require high reliability. Therefore, there has been a demand for a copper-based material that has the above-mentioned characteristic properties.
Brass and phosphor bronze are the principal materials for terminals and connectors. The former has an advantage in having very good formability and workability; but it is extremely poor in stress corrosion cracking resistance. Thus the use of brass is now under reconsideration from the standpoint of reliability. As a substitute for brass, more reliable phosphor bronze has come into general use and there is an increasing demand for it. This is because thin terminals and connectors are required as the electronic parts are miniaturized, particularly as the degree of integration of IC is increased, and electric appliances become lighter, smaller, and thinner than before. This holds true in the automotive industry, too. In addition, efforts are being made to discover new merits in copper-rich copper alloys.
Phosphor bronze, however, has some disadvantages. That is, it is expensive because it contains more than 3.0 wt% of tin, which is expensive, as shown in the Japanese Industrial Standards. It is poor in creep resistance at high temperatures. The heat resistance temperature is low, and the electrical conductivity is lower than 25% IACS.